The present invention relates to a light distribution control element, which can be used as a transmission type screen member in a rear projection type display apparatus or a viewing angle expanding member of a liquid crystal display apparatus or the like, and to a display apparatus using the light distribution control element.
A rear projection type display apparatus can comparatively easily produce a large screen display having a reduced size and at a low cost in comparison with a direct sight type CRT, and, therefore, its demand is increasing particularly in North American markets. Unlike a rear projection type display apparatus using a CRT projection tube, a highly fine display without any blur can be produced at peripheral portions of a screen by a dot matrix display, according to a rear projection type display apparatus having a projecting apparatus using a liquid crystal display element of the TN (Twisted Nematic) liquid crystal type or the like as a two-dimensional optical switch element; and, therefore, such a rear projection type display apparatus is expected to find use as a prospective component of a high resolution digital television.
FIG. 11 is a schematic sectional view of a rear rejection type display apparatus, in which a transmission type screen 703 is irradiated with a projected light beam 704 emitted from a projecting apparatus 701 via a mirror 702, and an image is displayed on a front face thereof.
As shown in FIG. 38, the transmission type screen 03 is normally constituted of a Fresnel lens sheet 1402 and a lenticular lens sheet 1401, and the Fresnel lens sheet 1402 is an optical element, which operates similar to a convex lens and has the function of widening the suitable viewing range by bending the direction of the main light beam from the projecting apparatus 701 toward an observer. The lenticular lens 1401 effectively distributes a limited projected light flux from the projecting apparatus 701 to an observing range of the observer to thereby provide a bright image as its object.
FIG. 36 is a schematic sectional view showing an example of a lenticular lens, and FIG. 37 is a schematic perspective view of the lenticular lens.
In the lenticular lens 1401, a plurality of cylindrical lenses 1501 are arrayed in one direction and black stripes 1502 are provided at portions other than portions for condensing a light beam, thereby restraining a reduction in the contrast ratio with regard to an ambient light beam without any loss of the projected light beam ideally by disposing the focal positions of the lenses 1501 on an observing face of the screen.
Generally, by arraying the lenticular lenses such that generators thereof are directed orthogonally to the display face, a wide viewing angle is provided in the horizontal direction. Therefore, a light beam is distributed in the vertical direction only by diffusion produced by a diffusing member blended in a base material of the lenticular lenses or surface portions thereof; and, accordingly, the viewing angle in the vertical direction is considerably narrower than that in the horizontal direction. Further, according to the lenticular lens, lenses having a linear shape are regularly arranged, and, therefore, moire interference fringe is liable to occur on the image.
In contrast thereto, Japanese Unexamined Patent Publication No. 2-77736 discloses a transmission type screen having a constitution in which a transparent base member 1601 is covered with spherical lenses 1602 which are fixed thereto by a transparent resin, as shown in FIG. 39. According to this constitution, no die is used, and therefore, there is no restriction in size in view of fabrication, and a seamless transmission type screen having a large screen surface can be realized. Further, a light beam incident from a side of the spherical lenses is converged by the lens effect of the spherical lenses and is diverged isotropically; and, therefore, wide viewing angles are provided both in the horizontal and vertical directions.
Further, there is a screen having a structure in which optical beads are fixedly attached on a transparent base member via a light-absorbing adhering agent layer, and wherein surfaces of the optical beads on the opposite side of the transparent base member are back-coated transparently, as described in SID94 DIGEST pp. 741-744 (A Novel High-Resolution Ambient-Light-Rejecting Rear-Projection Screen).
Further, Japanese Unexamined Patent Publication No. 9-318801 discloses a plane type lens having a structure in which very small spherical transparent beads are fixed on a transparent base member by a colored hot melt adhering agent layer and a transparent hot melt adhering agent layer. According to this structure, like the structure described in Japanese Unexamined Patent Publication No. 2-77736, due to the lens effect of the beads, the isotropic viewing angles are wide both in the horizontal and vertical directions. Further, an unnecessary light beam incident from outside is absorbed by a light-absorbing adhering agent layer (or colored hot melt adhering agent layer); and, therefore, a high contrast ratio is provided even in a bright environment. Further, high resolution can be realized comparatively easily by reducing the diameter of the bead.
The above-described conventional plane type lens (hereinafter, referred to as a light distribution control element) is fabricated as follows. A flat polyethylene terephthalate (PET)-resin film having a thickness of 120 xcexcm is used as the transparent base member; a transparent adhering agent layer comprising a polyester-based hot melt adhering agent is formed to a thickness of 5 xcexcm on a surface of the resin film; a colored adhering agent layer, in which the same polyester-based hot melt adhering agent is blended with 10 parts by weight of carbon black, is formed on the transparent adhering agent layer; and the entire structure is solidified.
Spherical transparent beads made of glass having a refractive index of 1.935 (wavelength: 589.3 nm) and a diameter of 50 xcexcm are densely arranged so as to be dispersed on the entire surface of the transparent base member. While heating the structure to soften the transparent adhering agent layer and the colored adhering agent layer in a thermostatic chamber, the transparent beads are pressed toward the transparent base member by a pressing plate, to thereby embed the transparent beads in and fixedly adhere them to the colored adhering agent layer and the transparent adhering agent layer. The thickness of the adhering layer after fixation is about 21 xcexcm, including the thicknesses of the transparent adhering agent layer and the colored adhering agent layer, and the transparent beads are exposed from the adhering agent layer by about 58% of the diameter thereof.
When the fabricated light distribution control element is evaluated as a transmission type screen of a rear projection type display apparatus having a projecting apparatus using a TN type liquid crystal display element as a two-dimensional optical switch element (light bulb), there are provided wide viewing angles equal to or larger than 50 degrees (in this case, an angle giving a brightness half of a front brightness) both in the horizontal direction and the vertical direction, and an unnecessary light beam incident from outside (an observer side) on the light distribution control element is absorbed by the colored adhering agent layer, so that a black display at low brightness can be realized even in a bright environment.
However, when an image projected on the light distribution control element is observed in an oblique direction, it is found that a fringe pattern substantially in the shape of concentric circles emerges and the image quality is significantly deteriorated. Further, it is also found that, when observed in an oblique direction, a change in chromaticity unfavorable to the image is caused.
It is an object of the present invention to provide a light distribution control element that does not produce any deterioration in image quality caused by the occurrence of the above-described fringe pattern, and to provide a display apparatus having high brightness, a high contrast ratio and a high viewing angle using the light distribution control element. Objects other than the above-described object will become more apparent from the following description.
The inventors have investigated in further detail the above-described conventional light distribution control element in order to find the cause of the occurrence of fringe patterns and the change in chromaticity. As a result, it has been found that the fringe pattern is produced when polarized light is incident on the light distribution control element; various phase differences are produced in light progressing at different angles in the transparent base member owing to optical anisotropy of the base member; and the fringe pattern is produced by a;difference between energy transmittances of a p polarized light component and an s polarized light component of light emitted from the transparent base member in combination with the phase difference. Further, it has been found that the change in chromaticity is caused since the light distribution characteristic of the light distribution control element is changed depending on the polarized state of incident light. The following is the gist of the present invention based upon the above-described findings.
[1] There is provided a light distribution control element including a transparent base member, a number of micro-lenses densely arranged on one face of the transparent base member and a light absorbing layer having very small opening portions substantially at focal positions of the micro-lenses, wherein the light distribution control element is characterized in that the transparent base member is constituted of a transparent body which is substantially isotropic optically or a transparent body having uniaxial optical anisotropy.
By using the light distribution control element, occurrence of a fringe pattern at the time of the incidence of polarized light is eliminated by restraining a phase difference which influences image quality from being caused.
[2] There is provided a rear projection type display apparatus including a projecting apparatus for projecting an optical image and a transmission type screen, on a rear face of which projected light from the projecting apparatus is incident, for displaying the projected light at a front face thereof. The rear projection type display apparatus is characterized in that the projecting apparatus comprises a single tube type projecting apparatus having a light source, two-dimensional optical switch elements for modulating light from the light source into an optical image in accordance with image information and a projecting lens for enlarging and projecting the optical image after the modulation; and, the projecting apparatus further comprises polarized light state aligning means for making polarized states of optical image lights formed by the two-dimensional optical switch elements substantially coincide with each other over the entire region of visible wavelengths, when the optical image after the modulation emitted from the projecting apparatus is incident on the transmission type screen. The transmission type screen is constituted of a light distribution control element, including a transparent base member, a number of micro-lenses densely arranged on one face of the transparent base member and a light absorbing layer having very small opening portions substantially at focal positions of the micro-lenses, the transparent base member being constituted of a transparent body which is substantially isotropic optically or a transparent body having uniaxial optical anisotropy, and a light flux collimating means provided on a projected light incident side of the light distribution control element.
As described above, the polarized states of the projected lights incident on the light distribution control elements (optical image lights) coincide with each other in the entire region of visible wavelengths. Accordingly, there is no staining derived from polarized light dependency of light distribution characteristics of the light distribution control element, so that there can be realized a display having a high image quality without any change in chromaticity, even when observed in an oblique direction.
Further, image light incident on the light distribution control element is brought into a substantially parallel state and is incident thereon substantially at an angle of incidence of 0 degree, and, accordingly, there is provided a bright display image by restraining any lowering of the transmittance of the light distribution control element.
[3] There is provided a rear projection type display apparatus, wherein the two-dimensional optical switch element is provided for producing a display by utilizing polarized light, the two-dimensional optical switch element comprising polarized light state converting means for converting a polarized light state of optical image light formed by the two-dimensional optical switch element into any of a polarized light state of linearly polarized light having an oscillation direction of an electric vector directed in a horizontal direction relative to a display face of the transmission type screen, linearly polarized light directed in a vertical direction, circularly polarized light and elliptically polarized light.
As described above, the polarized light state of the optical image light incident on the light distribution control element can be controlled; and, accordingly, there can be realized a rear projection type display apparatus in which the viewing angle characteristic can easily be changed by the polarized light dependency of the light distribution characteristic of the light distribution control element even when the constitution of the transmission type screen is not changed.
[4] There is provided a rear projection type display apparatus further comprising an observer sensing unit for sensing the presence or absence of an observer, observer position determining means for determining positions of the observer in the horizontal and vertical directions in response to a sensed signal received from the observer sensing unit, and control signal outputting means for outputting a control signal to a polarized light state converting element based on information provided by the observer position determining means.
As described above, a viewing angle characteristic can be attained in accordance with the positions of the observer by automatically determining the positions of the observer and changing the polarized light state of projected light based on position information that is, the viewing angle characteristic is automatically changed in accordance with the positions of the observer, so that limited image light is effectively distributed in a direction of the observer and excellent image is provided to the observer.
[5] There is provided a rear projection type display apparatus featured in that the projecting apparatus comprises a single tube type projecting apparatus having a light source, two-dimensional optical switch elements for modulating light from the light source into an optical image in accordance with image information and a projecting lens for enlarging and projecting the optical image after the modulation. The transmission type screen comprises a light distribution control element having a transparent base member, a number of micro-lenses densely arranged on one face of the transparent base member and a light absorbing layer having very small opening portions substantially at focal positions of the micro-lenses, and light flux collimating means arranged on a projected light incident side of the light distribution control element; and, the transmission type screen further comprises unpolarized light forming means for converting projected light emitted from the projecting apparatus and incident on the transmission type screen into substantially unpolarized light.
As described above, the optical image light incident on the light distribution control element constituting the transmission type screen is converted into unpolarized light; and, accordingly, there is no change in chromaticity derived from the polarized light dependency of the light distribution characteristic of the light distribution control element. Further, there is no fringe pattern produced at the time of incidence of polarized light by the optical anisotropy of the transparent base member of the light distribution control element; and, accordingly, a beautiful image can be provided without any deterioration in image quality. Further, even when a transparent body having optical anisotropy is used as the transparent base member, there is no deterioration in image quality; and, accordingly, the range of selection of the material is widened, and a transmission type screen can be realized comprising a light distribution control element which is inexpensive and is provided with high strength.
[6] There is provided a liquid crystal display apparatus including a pair of transparent substrates formed of a lamination of transparent electrodes and orientation films and bonded to each other with a constant clearance therebetween, while the faces on which orientation films are formed are opposed to each other. A liquid crystal layer is enclosed in the clearance, voltage applying means is provided for applying a voltage corresponding to an image signal across the transparent electrodes and a polarizer and an analyzer are disposed on a light incident face side and a light emitting face side of the pair of transparent substrates, respectively.
The liquid crystal display is characterized in that a rear face of each of the pair of transparent substrates is provided with a backlight apparatus for emitting substantially parallel light, and the light emitting face side of the pair of transparent substrates is provided with a light distribution control element comprising a transparent based member, a number of micro-lenses densely arranged on one face of the transparent base member and a light absorbing layer having very small opening portions substantially at focal positions of the micro-lenses. The light distribution control element has a transparent base member which is constituted of a transparent body which is substantially isotropic optically or a transparent body having uniaxial optical anisotropy.
Thereby, only light within a limited range in the vicinity of the front face, capable of achieving an excellent image quality, can be isotropically diverged by the light distribution control element; and, accordingly, a liquid crystal display apparatus can be provided which is capable of producing an image having a high contrast ratio without any change in chromaticity and no inversion of a gray scale within a wide viewing angle range.
[7] There is provided a liquid crystal display apparatus, wherein the light incident face side of each of the pair of transparent substrates is provided with a polarizer and the light emitting face side is provided with an analyzer and a light distribution control element in this order from the side of the transparent base member; and, the transmission axis of linearly polarized light of the analyzer is arranged in a horizontal direction relative to the display face.
In this way, by the polarized light dependency of the light distribution characteristic of the light distribution control element, the viewing angle in the horizontal direction becomes wider than that in the vertical direction relative to the display face and limited light can be effectively distributed to an observer.
[8] There is provided a liquid crystal display apparatus, wherein the light incident face side of the pair of transparent substrates is provided with a polarizer, the light emitting face side is provided with an analyzer and a light distribution control element in this order from a side of the transparent substrate, and a phase contrast plate is interposed between the analyzer and the light distribution control element.
Thereby, the polarized state of light incident on the light distribution control element can be arbitrarily changed by the phase contrast plate disposed between the analyzer and the light distribution control element; and, accordingly, by changing only the phase contrast plate, a desired viewing angle can be provided by utilizing the polarized light dependency of the light distribution characteristic of the light distribution control element.